This invention relates to a method and apparatus for controlling the dispensing of fluid, and more particularly, to a means for controlling the intravenous administration of a desired dose of fluid into a body.
The present invention is concerned with controlling the dispensing of fluid and is primarily concerned with the intravenous administration of a desired dose of fluid into the body of a patient. In the prior art, apparatus used for the intravenous administration of fluid have been generally of two basic varieties. The most common intravenous administration device is of the gravity flow type in which the rate of delivery of fluid is adjusted by means of a variable restriction. In such gravity flow systems, the variable restriction is usually provided by a clamping device that deforms a resilient fluid delivery tube connected to the hypodermic needle through which the fluid is introduced into the vascular system of the patient. The gravity flow types of devices may vary widely in cost and in the manner and complexity for controlling the flow rate of the fluid delivered to the patient.
It has been found that such gravity flow devices employing a variable restriction are incapable of reliable and uniform operation due to a number of factors, such as, the tendency of the plastic delivery tube to be subject to delayed plastic flow under stress, the variations in the hydrostatic pressure from the volume of fluid to be administered, variations in fluid viscosity, and changes in physical position and vascular pressure of the patient that may occur during administration of a quantity of fluid. In the gravity flow types of devices, the adjustment of the variable restriction governing the flow rate may be required to be performed manually, which is time consuming and subject to erroneous adjustment. Also, it is desirable for a doctor or nurse to frequently check the flow rate in administration of fluid in such devices to make sure that it is properly regulated. Moreover, a possible serious problem may occur in use of these types of devices when a complete stoppage of flow of fluid takes place, if the device is unattended at the time of exhaustion of the fluid. The unattended stoppage of flow of fluid at the needle in the patient may result in a blood clot which may cause a dangerous condition for the patient.
The other common variety of intravenous administration device is of the pump type which was designed to overcome various disadvantages of the gravity flow types of intravenous administration devices. Many different and complicated arrangements have been developed for regulating the pumping action and the quantity of fluid discharged. In the prior art, much design effort has been exerted to overcome the inherent capacity of the pump to force air into the patient with possible fatal consequences. The pump type of intravenous administration device has tended to be expensive, cumbersome, and complicated in structure. Further, these devices have been dependent upon a source of power greater than can be reliably and economically supplied by a battery. Various clinical reasons exist for avoiding the use of alternating current sources of power with intravenous administration devices, such as, electro-magnetic interference created by the power supply interfering with sensitive clinical devices and electrical impulses from the electrical systems for the pump devices being transmitted through intravenous fluid, which may be electrically conductive, to patients having sensitive heart conditions.
Accordingly, it is an objective of the present invention to provide an intravenous administration apparatus which is inexpensive and simple to operate while administering a desired dose of fluid in an accurately controlled manner. In order to accomplish this objective, it is desirable to provide a method and associated apparatus for intravenous administration of fluid at an accurately controlled rate irrespective of variables, such as, the level of fluid in the source, the venous pressure of the patient, and the viscosity of the fluid. Furthermore, it is desirable to provide an intravenous administration apparatus which enables automatic and progressive reduction of the rate of administration of the fluid at or near the time the desired dose has been administered and before complete exhaustion of the fluid in the administration apparatus so that air is not injected into the patient and blood clotting at the point of administration is prevented.
It is desirable to provide an intravenous administration apparatus which is small in size, light in weight, easily portable, and rugged in design. It is also desirable to provide such apparatus which includes a reusable timer capable of a long expectancy of use and a small, portable, replaceable power supply capable of supplying power to the apparatus. It is further highly desirable to provide an intravenous administration apparatus in which the parts of the apparatus through which the fluid passes is provided by a disposable unit, which is replaced after each use for easily maintaining the apparatus in a sterile condition. Moreover, it is desirable to provide an intravenous administration apparatus in which the parts of the apparatus are adapted to cooperate together in operative relationship only when the apparatus is properly assembled and conditioned for safe administration of fluid and provide such an apparatus which minimizes the likelihood of error by the person responsible for performing the intravenous administration of fluid to the patient.